| 摘要 |
PROBLEM TO BE SOLVED: To realize compatibility between economy and heater control in each semiconductor manufacturing step, by preparing a plurality of thyristor control systems and switching these systems therebetween for each step. SOLUTION: Power to be supplied to a heater 15 is determined by a temperature control circuit 21 on the basis of an in-furnace temperature and a heater temperature and controlled by a thyristor circuit 19. A plurality of control signal generation means for applying a gate signal to the thyristor circuit 19 are prepared to be switched therebetween by a switch means 37. The control signal generation means includes a zero-crossing control signal generation means and time-division dispersion zero- crossing control signal generation means 35 and 36 for turning ON and OFF an A.C. power alternately at each one cycle of the power or at each half cycle thereof. According to the switching, an execution step requiring a stable temperature state selects phase control, an initial and later stable step selects zero-crossing control to realize an economical efficiency, a temperature raising step in a semi-execution process state selects semi-period time-division dispersion zero-crossing control reasonable in economical efficiency and control performance, and a lowering temperature step selects one- period time-division dispersion zero-crossing control allowing a slightly increased economical efficiency.
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